In recent years, thin televisions such as a liquid crystal television and a plasma television are widely used. Further, the start of digital broadcasting has been increasing demand for large televisions. Among such large televisions, there is a high demand for high-definition televisions and full high-definition televisions, and so-called wide-screen televisions having an aspect ratio of 16:9 dominate a majority.
On the other hand, in view of the housing conditions in Japan, an entire television set is desired to be narrow and thin.
A television loudspeaker unit is usually attached to both sides of an image display device so as to output stereo sound with improved effect, which contributes to the increase in width of the entire television set.
Thus, conventionally, loudspeakers commonly included in a television loudspeaker unit are of elongated shapes (hereinafter referred to as a “narrow loudspeaker”) such as rectangular or elliptical. Further, demand is strong for even narrower loudspeakers because of the increase in width of image display devices, while demand is also strong for narrow loudspeakers, having high sound quality that are capable of reproducing dynamic sound commensurate with the dynamism of the large screens. Furthermore, image display devices have also been being reduced in thickness, and therefore there is also a demand for the reduction in thickness of narrow loudspeakers.
Here, the following is a description of a conventional typical narrow loudspeaker. FIG. 26(a) through (c) is a diagram showing the structure of a conventional narrow loudspeaker. FIG. 26(a) is a plan view; FIG. 26(b) is a cross-sectional view taken in the longitudinal direction (c-c′); and FIG. 26(c) is a cross-sectional view taken in the transverse direction (o-o′). A narrow loudspeaker 100 shown in FIG. 26(a) through (c) includes a magnet 101, a plate 102, a center pole 103, a frame 104, a voice coil bobbin 105, a voice coil 106, a damper 107, a diaphragm 109, a dust cap 110, and an edge 111. Further, magnetic gaps 108 are formed with the magnet 101, the plate 102, and the center pole 103.
The voice coil 106 is a winding formed of a conductor such as copper or aluminum, and is fixed to the cylindrical voice coil bobbin 105. The voice coil bobbin 105 supports the voice coil 106 so as to suspend the voice coil 106 within the magnetic gaps 108. The voice coil bobbin 105 is connected to the frame 104 through the damper 107. The voice coil bobbin 105 is adhered to the diaphragm 109 on the opposite side of the voice coil bobbin 105 to that on which the voice coil 106 is fixed to the voice coil bobbin 105, the diaphragm 109 being of an elliptical or generally elliptical shape. The dust cap 110 is fixed to the central portion of the diaphragm 109, and has a cross section of a generally semicircular shape. The edge 111 is of a loop shape and has a cross section of a semicircular shape, and the inner peripheral portion of the edge 111 is fixed to the outer peripheral portion of the diaphragm 109. The outer peripheral portion of the edge 111 is fixed to the frame 104.
In order to drive the narrow loudspeaker 100, alternating current is applied to the voice coil 106. Then the voice coil bobbin 105 makes piston movements based on the alternating current flowing through the voice coil 106 and the magnetic field produced around the voice coil 106, and thereby the diaphragm 109 vibrates in the direction of the piston movements. Consequently, sound waves are emitted from the diaphragm 109.
Patent Literature 1 discloses a loudspeaker having a similar structure to that of the narrow loudspeaker 100. FIG. 27 is a diagram showing the frequency characteristics of the reproduction sound pressure level of the conventional narrow loudspeaker disclosed in Patent Literature 1. The vertical axis represents the reproduction sound pressure level obtained at the point 1 m away from the loudspeaker on an axis extending forward therefrom when 1 W is input thereto, and the horizontal axis represents the driving frequency.